The right of priority under 35 U.S.C. xc2xa7119(a) is claimed based on German Patent Applications No. 101 00 252.1, filed Jan. 5, 2001, No. 201 15 273.8, filed Sep. 15, 2001, No. 101 45 658.1, filed Sep. 15, 2001, and No. 101 50 896.4, filed Oct. 18, 2001, the disclosures of which are hereby incorporated by reference. This application is related to U.S. application Ser. No. 10/024,627, filed concurrently herewith, which is also incorporated herein by reference.
The present invention relates to an air-conditioner for a motor vehicle and to a heat exchanger, especially an evaporator, suitable for use in an automotive air-conditioner.
Motor vehicle manufacturers are seeking to reduce the fuel consumption of their vehicles. One measure for reducing the fuel consumption is to cut off the engine While being at a temporary standstill, such as when stopping at a traffic light, for example. This temporary engine cut-off is also known as the idle-stop mode. This measure is already used in present-day fuel-saving vehicles, such as the so-called xe2x80x9cthree-literxe2x80x9d vehicle, for example. In vehicles having the idle-stop operating mode the engine is shut off for approximately 25-30% of the journey time in urban traffic.
This is one reason why such vehicles are not equipped with an air-conditioner. With the engine shut off, the compressor, which is essential to an air-conditioner, cannot be powered, and therefore in the idle-stop mode an air-conditioner cannot provide the necessary refrigeration capacity.
To solve this problem, it is proposed in EP 0 995 621 A2 to use the condensate produced in the cooling of moist air to ice-up the evaporator of the air-conditioner, so that in the idle-stop mode, when the engine is shut off, the air can be cooled by the then melting ice. This method has numerous disadvantages, however. The quantity of water that is present in the air and is needed for icing-up of the evaporator varies as a function of the ambient climatic conditions. Thus, it may happen that with low air humidity there is insufficient condensation water available to ice-up the evaporation. Furthermore, a relatively long period of time is generally needed for icing-up of the evaporator, so that this known air-conditioner can function in idle-stop mode only after a relatively long driving time. Another problem is that the evaporator generally ices-up unevenly, so that the evaporator has some areas that are iced-up and some areas that are not. Furthermore, icing may be so intense that the air can flow through the evaporator only with a high pressure loss, if at all. In any case, the layer of ice produces a pressure loss on the air side, which leads to the need for an increased blower output. Another disadvantage is that bacteria readily settle on moist surfaces and cause unpleasant odors.
One principal object of the invention is to provide an improved air-conditioner having a heat exchanger, especially an evaporator, which delivers refrigeration capacity even with the compressor shut off.
A further object is to provide an air-conditioner, which ensures air-conditioning of the vehicle under all operating and ambient conditions, including the idle-stop situation.
In accomplishing these and other objects, there has been provided according to one aspect of the present invention an air-conditioner for a motor vehicle, comprising: a primary refrigerant circuit through which a refrigerant circulates, the primary refrigerant circuit including a heat exchanger through which the refrigerant flows, and the heat exchanger including therein a secondary internal refrigerant circuit that operates when the primary refrigerant circuit is at a standstill.
In accordance with another aspect of the invention there has been provided a heat exchanger suitable for use in an air-conditioner of a motor vehicle, comprising: a plurality of passageways for transporting an air-conditioning refrigerant, the passageways having an upper end and a lower end when mounted in a motor vehicle; and a cold store arranged near the upper ends of at least some of the heat exchanger passageways.
Further objects, features and advantages of the present invention will become apparent from the detailed description of preferred embodiments that follows, when considered together with the accompanying figures of drawing.